RX 580 hits 80c and pc black screens

[Salad Phd]

Greentings! 
 

i have an XFX rx 580 and recently when i play games as soon as the card reaches 82-83 degrees, the pc black screens and i have to restart. 

i undervolted the card by -30% in afterburner and played around with the power curve to the point that the card is stable and i have no problem putting the fans on 70% manually and play for hours.

but at auto fan curve, the card reaches 80c and in terms of seconds, the pc black screens.

i fairly cleaned the card since it was a mining unit and re-paste it with CoolerMaster Mastergel Pro v2 

but i noticed that the thermal pads on vrm and vram are also dusty (it’s not crusty it’s just dusty) could it be that the pads are bad ? 
the idle temps are 50-55c (at 55 the 0db mode turns off until the card reaches 49-50 again) which is high in my opinion even for an xfx card 

could it be that i need to repaste the card ? 
Pc specs: 

ryzen 3 3300x at 3.9 ghz via ryzen master 

16 gig 3400mhz 

450 watts 80p bronze ( i know the psu is a little weak for this config )

 

i want to know that if my card is healthy and my problems are caused by a weak psu/bad paste application since i only have budget to replace either my gpu or psu 

 

I hope my card is ok because i play for hours and hours without any weird stuff on background when i set my fan curve at 70-80% manually 

But as soon as i let it ramp up automatically, it reaches 81-83c in AAA /Heavy FPS titles and blackscreen And i’m in desperate need for help !

[Adept_Austin]

Do you have a second power supply handy? You could plug that up outside the case and power the GPU from the secondary PSU. If the PC runs through any benchmarks/gaming without any trouble, then that would signal a PSU issue to me. You could also take your GPU to a friend with a more powerful PSU and see if there's any trouble on their machine. If there are issues in that config, then it's probably the GPU.